An occlusive consonant is a type of obstructive consonant sound produced by a cessation of airflow and its subsequent release.
The occlusive consonants are divided into six phonemes divided into two series:
- three deaf p, t, k
- three sound b, d, g
Both series contain the same three points of articulation:
- bilabial p, b
- dental t, d
- velar g, k
Any of these consonants causes the air to be released in an explosive manner producing a small «pop» sound, hence the name «pop filter». Not only does this happen with these in particular, the sibilances and the occlusions, but also this type of problem usually occurs when we record words as a whisper.
A sibilant is a type of fricative consonant that is articulated, projecting a jet of air, along a narrow channel, formed by the tongue in the oral cavity, that ends in an obstacle, like the teeth, which generates a strident sound.
Within the group of sibilant consonants is the letter S, which has most of its energy around 8,000 Hz, and can even have an emission in the 10,000 Hz band. Then we find the letter F, which has the bulk of its emission around 4,000 Hz, but can reach up to 8,000 Hz.
What to do during recording?
Generally when recording voices, it is done with close microphones, this means that it is no more than 30 cm (one quarter) from the sound source.
If you notice that the person you are recording has a lot of occlusive, frictional or wheezing problems you can practice the following tips:
- Record with a high-quality dynamic microphone rather than a condenser microphone, as these microphones, usually found in studios, tend to be more sensitive.
- Have an «anti-pop» filter for the microphone.
- Configure the microphone so that the speaker is outside the central axis of the microphone pick-up pattern, i.e. does not speak directly but from the side. This causes the force of the occlusives and hissing to be reduced because the air enters at an angle and not from the front.
- Use a De-Esser plug-in during recording on a side channel. This plugin is a compressor with an equalizer chained to it. This means that it works as a compressor would, but only for the specific frequency range assigned to it. Attention! Here you have to be very careful to set the threshold at the right point.
What to do during editing and mixing?
Occlusives and wheezing are in a certain range of the frequency spectrum:
- Occlusive: 150 Hz/200 Hz > or less
- Sibilants: 6 KHz – 8 KHz < or higher
This is why equalization is fundamental when it comes to correcting both.
- It is almost always useful to apply a High Pass Filter for the occlusives.
- A Low Pass Filter for the sibilants/frictives.
In order to know how to equalize each of the problems it is advisable to have an open spectrogram to be able to see where and what frequencies are most affected, both in occlusive and sibilant, in order to be able to treat them with equalizer or filters and thus be able to be more accurate.
- Use volume automation to lower the intensity. This is a very careful edition that will give the best results, if done with the treatment and precision of a surgeon.
These simple tips are the ones that will help us avoid and diminish the problems of occlusives and sibilants so as not to go crazy and fight too much in the art of voice editing.
Author: Sol Rezza
Editor | Corrector: Franco Falistoco